Fume treatment system and method

ABSTRACT

A fume treatment system and method for treating a fume stream emitted from the mouth of a furnace chamber of a metal reclamation furnace system during a portion of the reclamation process includes an auxiliary hood that is smaller than the main overhead hood and is movable between an operative position over the furnace chamber mouth within the main overhead hood for collecting the fume stream emitted by the furnace chamber mouth and another position spaced from, the furnace chamber mouth. An incinerator is in fluid communication with the auxiliary hood when in the operative position. A fume stream blower causes the fume stream collected by the auxiliary hood when in the operative position to flow to the incinerator for incinerating hydrocarbons or other combustible compounds present in the fume stream during operation of the incinerator. A cyclone may be in the flow path between the auxiliary hood and the incinerator for removing particulates from the fume stream prior to entering the incinerator. Also a heat exchanger may be downstream of the incinerator for reducing the temperature of the fume stream exiting the incinerator prior to returning the fume stream to the main overhead hood for further processing.

FIELD OF THE INVENTION

This invention generally relates to a system and method for treating the fume stream from furnaces including particularly tilting rotary furnaces used in the reclamation of ferrous or non-ferrous metals such as aluminum from scrap or dross.

BACKGROUND OF THE INVENTION

During the reclamation of ferrous or non-ferrous metals such as aluminum from scrap, the removal of particulate material and volatile pollutants such as hydrocarbons and other combustible compounds including volatile organic compounds (VOCs) from the fume stream rendered by the scrap is oftentimes a problem. Usually the cheaper the scrap, the more the scrap gives off these particles and pollutants. These fume streams can generally be converted to forms of emissions that are within the acceptable limits of pollution control regulations using an afterburner arrangement to incinerate or oxidize the hydrocarbons or other combustible compounds (including VOCs) in the stream.

There are two types of commonly used afterburner configurations. One type is a direct-fired catalytic oxidizer that utilizes an afterburner to preheat the gas stream for catalytic combustion of compounds which are ordinarily difficult to combust. The other type, which is more commonly used, is a direct-fired afterburner that has proven to be an acceptable way of controlling combustible emissions from various industrial processes.

However, in the case of metal reclamation furnace systems that utilize a main large overhead hood to capture the fume stream, the capture velocity dictates high air flows. The burner to control and operate an afterburner incinerator to treat this magnitude of air flow is quite large and expensive. Further there is the problem of how to treat the large amounts of hot air coming out of an afterburner incinerator. If all of these hot gases are directed into a bag house to remove the non-combustible particles therefrom, the bag house would have to be substantial to be able to sustain the high temperature of the hot gases passing therethrough. Alternatively, if the hydrocarbons and other combustible compounds are not incinerated out of the air stream prior to entering the bag house, the combustible compounds that are collected in the bag house have the potential to cause a bag house fire.

SUMMARY OF THE INVENTION

The system and method of the present invention are designed to capture and incinerate only the portion of the fume stream emitted from the furnace chamber during the metal reclamation process that contains the majority of the hydrocarbons and other combustible compounds (including VOCs), not the entire volume of the air stream collected by the main large overhead hood during the reclamation process. This minimizes the volume of gases the fume treatment system is required to process. Moreover, since the majority of the volatile compounds have been removed from the air stream prior to entering the bag house, the possibility of an exothermic reaction during post processing of the air in the bag house or other post treatment system is significantly reduced. Also this may permit a reduction in the size of the bag house or any other post treatment system required to treat the air stream.

In accordance with one aspect of the invention, the fume treatment system includes an auxiliary hood that is much smaller than the main overhead furnace hood and is movable into and out of an operative position over the furnace mouth within the main overhead furnace hood.

In accordance with another aspect of the invention, an incinerator and blower are in fluid communication with the auxiliary hood when in the operative position, whereby when the blower is activated, a draft is induced in the auxiliary hood causing the fume stream emitted by the furnace chamber to flow to the incinerator where hydrocarbons or other combustible compounds in the fume stream are incinerated during operation of the incinerator.

In accordance with another aspect of the invention, a cyclone may be in the fume stream between the auxiliary hood when in the operative position and the incinerator for removing particulates from the fume stream prior to the fume stream being incinerated in the incinerator.

In accordance with another aspect of the invention, a heat exchanger may be in the fume stream downstream of the incinerator for quenching the fume stream after exiting the incinerator within a period of time that also retards the formation of dioxins.

In accordance with another aspect of the invention, the fume stream blower may be upstream of the heat exchanger but is preferably downstream of the heat exchanger where the air stream is considerably cooler.

In accordance with another aspect of the invention, the fume stream downstream of the heat exchanger may be directed back to the main overhead furnace hood for post treatment processing.

In accordance with another aspect of the invention, the fume stream that is directed back to the main overhead furnace hood from the heat exchanger may be combined with ambient air to further reduce the fume stream temperature.

In accordance with another aspect of the invention, the incinerator may comprise a direct-fired afterburner including a burner assembly, a combustion chamber, and means for modulating gas flow to the burner assembly during incineration of the fume stream to maintain a predetermined temperature range in the combustion chamber.

In accordance with another aspect of the invention, a flow control valve may be provided in the fume stream for modulating the fume stream to the incinerator based on the fume stream temperature downstream of the incinerator.

These and other objects, advantages, features and aspects of the invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter more fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail a certain illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principles of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a tilting rotary furnace system provided with the fume treatment system of the present invention;

FIG. 2 is an enlarged fragmentary perspective view showing an auxiliary hood of the fume treatment system positioned over the furnace chamber mouth within the large main overhead furnace hood for collecting the fume stream emitted from the furnace chamber mouth during charging of the furnace chamber with scrap material;

FIG. 3 is an enlarged fragmentary perspective view showing the furnace chamber door in the closed position and the auxiliary hood positioned over the furnace chamber mouth and the door flue for collecting the fume stream emitted through the door flue during the initial melt cycle;

FIG. 4 is an enlarged fragmentary perspective view similar to FIG. 3 but showing the auxiliary hood moved to an out of the way inoperative position in spaced relation from the furnace chamber mouth;

FIG. 5 is an enlarged fragmentary longitudinal section through an end of a fluid duct on the auxiliary hood in sealed engagement with an end of another fluid duct in fluid communication with an incinerator downstream of the auxiliary hood when the auxiliary hood is in the operative position shown in FIGS. 2 and 3;

FIG. 6 is an enlarged fragmentary longitudinal section similar to FIG. 5 but showing the end of the fluid duct on the auxiliary hood pivoting toward or away from the end of the other fluid duct during movement of the auxiliary hood into or out of the operative position shown in FIGS. 2 and 3;

FIG. 7 is a perspective view of the incinerator of the fume treatment system to which the auxiliary hood is connected when in the operative position;

FIG. 8 is a side elevation view of the incinerator of FIG. 7;

FIGS. 9 and 10 are respective left and right end views of the incinerator of FIG. 8; and

FIG. 11 is a block flow diagram of the fume treatment system of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now in detail to the drawings, and initially to FIG. 1, there is shown by way of example a tilting rotary furnace system 1 used to recover a metal from scrap material containing the metal or from dross material containing the metal obtained from some other industrial process. The scrap or dross material (collectively referred to herein as scrap material) containing the metal along with flux material is charged into the furnace chamber 2 and melted to separate and recover the desired metal. Dross, as used herein, may include the solid scum that forms on the surface of a metal when molten or during melting, and is largely the result of oxidation, but may also include other impurities that rise to the surface of the mixture. Dross may also include a mixture of salt, flux and waste or foreign matter mixed with a substance or what is left as a residue after the substance has been used or processed. A common non-ferrous metal that is recoverable using such a furnace system is aluminum or aluminum alloys (collectively referred to herein as aluminum). However, it should be understood that such a furnace system can also be used to reclaim other non-ferrous or ferrous metals from scrap containing the metals as well.

The furnace system 1 may, for example, be generally of the type disclosed in U.S. Pat. No. 6,395,221, the entire disclosure of which is incorporated herein by reference. In general, the furnace system 1 is operated as follows. One or more furnace feeder charge carts 3 containing the scrap material are moved into position adjacent the mouth 4 of the furnace chamber 2 as shown in FIG. 1. Then, with the furnace door 5 open, the charge material is loaded into the furnace chamber through the open mouth 4 using a charging unit 6 such as a conveyor or other loading mechanism as shown in FIG. 2. Afterwards the feeder carts 3 are withdrawn and the furnace door 5 is closed. The furnace chamber 2 is then rotated and heated so the metal becomes flowable or in a near molten state. This process of charging the furnace chamber with charge material and melting the charge material may be repeated several times if desired.

Once the furnace chamber has been charged to the extent desired and the total quantity of charge material within the furnace chamber is sufficiently flowable, or molten, the furnace chamber door 5 is opened and the furnace chamber 2 is unloaded in a decanting type action by actuating one or more fluid actuators 7 to raise the rear end 8 of the furnace chamber about a pivot 9 adjacent the front end 10 of the furnace chamber to cause the molten metal to flow out of the furnace chamber mouth 4 into a recovery container (not shown). After the molten metal has been poured out of the furnace chamber, the remaining waste material or slag may be removed from the furnace chamber by further tilting the rear end of the furnace chamber upwards and rotating the furnace chamber in the same or different directions at the same or different speeds as desired.

During the reclamation of metals including particularly non-ferrous metals such as aluminum from scrap, the removal of particulate material and gaseous pollutants including hydrocarbons and other combustible compounds (including volatile organic compounds (VOCs)) from the fume stream rendered by the scrap material is oftentimes a problem. Usually the cheaper the scrap material, the more the scrap material contains these combustible compounds.

Traditionally the fume stream rendered by the scrap material is diluted in the main large overhead hood 11 located over the furnace chamber mouth 4 and exhausted to an incinerator where the entire air stream is incinerated. In such a large overhead hood 11 where the capture velocity dictates high air flows, the burner needed to control and operate an incinerator large enough to treat the entire volume of the air stream collected by the overhead hood is quite large and expensive. Also there is the additional problem of how to treat the large amounts of high temperature exhaust gases from the incinerator. If for example all of these hot gases are directed into a bag house to remove the particulates therefrom, the bag house would have to be substantial to sustain the high temperature of the hot gases passing therethrough. Alternatively, if an incinerator is not used to incinerate the fume stream before the fume stream is directed to the bag house, the combustible compounds that are collected in the bag house would have the potential to cause a bag house fire.

To overcome these problems, the fume treatment system 15 of the present invention captures the fume stream emitted from the furnace chamber 2 in a much smaller hood 16 than the main overhead hood 11 during material charging of the furnace chamber and during the initial melt cycle of the charge material within the furnace chamber. This is when a majority of the VOCs and other combustible compounds are rendered from the charge material. The fume stream containing the majority of the VOCs and other combustible compounds is captured by the smaller auxiliary hood 16 with minimal tertiary air and directed to an incinerator 17 (see FIG. 1) where the fume stream is heated to a sufficiently high temperature for a sufficient length of time to incinerate a majority of the VOCs and other combustible compounds in the fume stream as described hereafter. Capturing the fume stream in this way prior to the stream being diluted in the main large overhead hood 11 minimizes the size of the burner system needed to incinerate the majority of the combustible compounds rendered by the charge material during the reclamation process.

In the case of a large main overhead hood where the capture velocity dictates high air flows, the resultant volume may be in the range, for example, of approximately 16,000 cfm. The incinerator burner for a system of this magnitude would be approximately 30 mm BTU/hr., which is quite large and expensive to operate. In contrast, the fume treatment system 15 of the present invention, which captures the fumes at the source with minimal tertiary air, requires a much smaller incinerator burner, on the order of approximately 5 mm BTU/hr., to destroy the combustible compounds in the fume stream. Minimizing the volume of fumes that the fume treatment system is required to handle reduces the size of the bag house and any post treatment system required.

The smaller auxiliary hood 16 may be supported within the large main overhead hood 11 by a support frame 18 that may be pivotally connected by hinge brackets 19 to suitable fixed support members 20 within the main overhead hood. This allows the auxiliary hood 16 to be pivoted between the operative position shown in FIG. 2 over the furnace chamber mouth 4 (and over the door flue 21 when the furnace door 5 is closed as shown in FIG. 3) to an inoperative out of the way position in spaced relation from the furnace mouth as shown in FIG. 4 where the auxiliary hood won't interfere with the tilting of the furnace chamber during unloading in the manner previously described. Alternatively, the auxiliary hood 16 may be moved laterally, rather than pivoted, between the operative and inoperative positions. When in the operative position, the sides 22 of the retractable hood 16 may extend part way around opposite sides 23 of the door flue 21 in close proximity to the furnace mouth 4 and still provide sufficient clearance between the auxiliary hood and the furnace chamber door 5 as shown in FIG. 3 to allow the furnace chamber door to be opened and closed while the auxiliary hood remains in the operative position.

Mounted on the auxiliary hood 16 is a fluid conduit or duct 25 in fluid communication with the interior of the hood. Duct 25 may extend outwardly toward the pivotal connection 19 between the auxiliary hood and the fixed support members 20 to provide for swinging movement of its outer end 27 toward and away from an end 28 of another duct 29 during pivotal movement of the auxiliary hood toward and away from the operative position. Duct 29 may extend through a wall 30 of the main overhead hood 11 and is in fluid communication with the incinerator 17. Duct end 28 may have a steel angle 31 attached to its inner wall for supporting a suitable gasket 32 thereon for sealed engagement by a ring 33 extending from the outer end 27 of the auxiliary hood duct 25 as shown in FIG. 5 when the auxiliary hood is in the operative position shown in FIGS. 2 and 3. FIG. 6 shows the outer end 27 of the auxiliary hood duct 25 pivoting toward or away from the duct end 28 during movement of the auxiliary hood 16 toward and away from the operative position.

As seen in FIG. 1, a fan or blower 34 may be provided in the fume stream to provide the necessary draft for transporting the fume stream through the fume treatment system 15. In the process of fume collection by the auxiliary hood 16, a proportional quantity of tramp or ambient air is also pulled into the auxiliary hood by the fan 34, which may be used as a supplemental oxygen supply for the incinerator combustion process. Also, a cyclone 35 may be provided in the fume stream between the auxiliary hood 16 and the incinerator 17 to remove particulates from the fume stream before the VOCs and other combustible compounds in the fume stream are incinerated in the incinerator.

From the incinerator 17 the thermally treated exhaust stream may be routed through a duct 36 to a heat exchanger 37 where the exhaust stream is quenched within a period of time that also retards the formation of dioxins. The heat exchanger can be air-to-air or a direct contact exchanger such as a regenerator. From the heat exchanger the fume stream may be routed through a duct 38 to the main overhead hood 11 where the fume stream may be collected along with additional tramp or ambient air that is drawn into the main overhead hood and any fugitive emissions from the furnace chamber 4 to further reduce the overall stream temperature to within the operating limits of the bag house or any other post treatment system required. Since the majority of the volatile compounds are removed from the fume stream by the fume treatment system 15 of the present invention prior to entering the bag house, the possibility of an exothermic reaction in the bag house is significantly reduced, thus reducing the size of the bag house and any post treatment system required. Also maintaining a relatively low temperature at the inlet to the bag house means less maintenance of the bag house.

The blower or fan 34 used to transport the fume stream through the fume treatment system 15 may be located upstream or downstream of the heat exchanger 37 but is preferably located downstream of the heat exchanger where the air stream is considerably cooler. This reduces the size of the fan 34 required to transport the fume stream through the fume treatment system as well as the required maintenance of the fan.

The incinerator 17, shown in greater detail in FIGS. 7-10, may be a direct-fired afterburner arrangement including an oxyfuel lance burner 40, a combustion chamber 41 designed to provide adequate temperature and residence time for efficient fume destruction, and a burner control system including temperature regulation of the combustion chamber using fuel modulation. Combustion chamber 41 may have three flame zones, a primary flame zone 42 inside the burner 40 where the burner is run on excess oxygen, a secondary flame zone 43 inside a refractory lined Tee 44 where the fume stream comes in and mixes with the oxygen, and a third flame zone 45 where combustion takes place and provides sufficient residence time to complete the combustion process prior to exiting out the exit chamber 46. The destruction of the combustible fumes in the air stream is totally time and temperature dependent depending upon the chemical compounds and available oxygen present in the stream.

The oxyfuel burner 40 uses very little fuel because a significant portion of the fuel for the combustion process comes from the fume stream itself. Because the fume stream is so high in VOCs, the fume stream burns and contributes to its own destruction. Oxygen for the burner 40 may be air that is added directly into the burner or to the secondary combustion zone 43. However, pure oxygen is preferably used to enrich the primary combustion zone 42 for stable operation and complete oxidation of the fume stream. Also, oxygen or air may be added to the secondary combustion zone 43 for increased oxygen and to control combustion chamber temperature. However, it is easier to add pure oxygen to the fume stream than air. Also, it takes a much greater quantity of air to equal the quantity of oxygen needed to obtain the desired amount of oxygen for stable operation and complete oxidation of the fume stream.

The fume treatment system 15 may be designed in such a manner to enable automatic actuation of a fluid cylinder 47 (schematically shown in FIG. 11) to automatically move the auxiliary hood 16 into place over the furnace chamber mouth 4 once the temperature of the incinerator combustion chamber 41 reaches an arbitrary variable set point, for example of approximately 800° C. If the incinerator combustion chamber temperature falls below a variable set point, for example of approximately 700° C., the auxiliary hood 16 may automatically retract to the out of way position within the main furnace hood 11 shown in FIG. 4.

Purge of the incinerator combustion chamber 41 may be performed by operating the fume stream blower 34 for a variable predetermined time prior to beginning the incinerator ignition sequence. During purge, the fume stream control valve 50, shown in FIG. 11, may be open part way, for example, 60% open. The control skid should include all safety valves, leak test devices, high and low gas pressure switches, and comply with CE and all European regulations for both oxygen and gas. The burner pilot may use natural gas and compressed air as the oxidant. The compressed air may be left on continuously for purge of the pilot tunnel for UV sensing.

The main control for the incinerator 17 may be based on the output from a thermocouple 51 located in the incinerator to the control unit 52. If the set point of the thermocouple 51 is exceeded, the control unit may output a proportional signal to the incinerator modulating gas valve 53 decreasing its input. If the thermocouple 51 is below a predetermined set point, the control unit 52 will output a proportional signal to the gas valve 53 increasing gas flow.

The fume stream control valve 50 may be modulated to modulate the fume stream according to the input from a thermocouple 56 located in the fume stream upstream of valve 50. If the temperature of the fume upstream of valve 50 increases above a desired set point, the control unit 52 may output a proportional signal increasing the percentage of the opening in the valve 50. If the temperature decreases below a desired set point, the control unit may output a proportional signal decreasing the percentage of the opening in the valve 50.

If a second set point used as an over temperature blower safety set point is exceeded, the incinerator 17 will perform an emergency shutdown. An emergency shutdown of the incinerator because of high fume stream temperature may consist of the auxiliary hood 16 retracting to the out of the way position shown in FIG. 4. If the set point does not get satisfied within a predetermined time period, for example one minute, the control unit 52 may shut down the gas and oxygen safety shut off valves 57 and 58 and the fume stream blower 34. Likewise, a secondary control for this valve may be from a thermocouple located in the combustion chamber of the incinerator. If the temperature rises above the desired incinerator set point and the modulating gas valve 53 proportional signal is at its minimum, the fume stream control valve 50 may open wider until the incinerator combustion chamber 41 temperature set point decreases and satisfies the set point. If the incinerator combustion chamber temperature does not decrease to satisfy the set point, the system may perform an incinerator over temperature emergency shut down consisting of the auxiliary hood 16 moving to the out of the way position, shut down of the gas and oxygen safety shut off valves 57 and 58, and shut down of the fume stream blower 34.

The incinerator 17 may also include in addition to the control thermocouples, a redundant thermocouple to be used as a safety device for over temperature. If the redundant thermocouple set point is exceeded and the modulating gas valve 53 is at its minimum input and the fume stream control valve 50 is at its maximum open position for a predetermined period of time, for example five minutes, the incinerator system may perform the same emergency shut down as for incinerator over temperature.

The heat exchanger 37 may be a direct contact exchanger such as a regenerator or an air-to-air heat exchanger with a modulating control valve 60 for the cooling air that is received from a forced air blower 61. The temperature of the cooling air may be measured by a thermocouple 62 and controlled by the control unit 52. If the temperature of the cooling air rises above a predetermined set point, the control unit 52 may output a proportional signal to open the control valve 60 of the cooling air, increasing flow, whereas if the temperature drops below the set point, the control unit 52 may output a proportional signal to close the control valve 60 of the cooling air, reducing flow.

Once the incinerator combustion chamber 41 temperature reaches a desired variable set point of, for example, 800° C., and the auxiliary hood 16 has been moved into the operative position over the furnace chamber mouth 4 in the manner previously described, the fume blower 34 will capture the fume stream that is emitted during charging of the furnace chamber 2 in the auxiliary hood for incineration in the incinerator 17. After the charge has been made to the furnace chamber 2, the feeder cart 3 is withdrawn and the furnace chamber door 5 is closed, with the auxiliary hood 16 remaining in place over the door flue 21 to collect the fume stream that is emitted through the door flue during the initial melt cycle while the main furnace burner (not shown) is set to low fire, and the furnace chamber 2 is rotated at a relatively slow speed to control the release of the volatile compounds for incineration in the incinerator 17. At the end of the melt cycle, which typically takes about twenty minutes, the VOCs are virtually no longer being rendered by the charge material. Accordingly, at this point the auxiliary hood 16 may be retracted out of the way and the incinerator 17 shut down to avoid incinerating the furnace chamber gases indefinitely.

Although the invention has been shown and described with respect to a certain embodiment, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of the specification. In particular, with regard to the various functions performed by the above described components, the terms (including any reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed component which performs the function in the herein illustrated exemplary embodiment of the invention. Also, all of the disclosed functions may be computerized and automated as desired. In addition, while a particular feature of the invention may have been disclosed with respect to only one embodiment, such feature may be combined with one or more other features as may be desired and advantageous for any given or particular application. 

1. A fume treatment system for treating a fume stream emitted from the mouth of a furnace chamber of a metal reclamation furnace system during a portion of the reclamation process, the furnace system having a main overhead hood located over the furnace chamber mouth, the fume treatment system comprising an auxiliary hood that is smaller than the main overhead hood and is movable between an operative position over the furnace chamber mouth within the main overhead hood for collecting the fume stream emitted by the furnace chamber mouth and another position spaced from the furnace chamber mouth, an incinerator in fluid communication with the auxiliary hood when in the operative position, and a fume stream blower for causing the fume stream collected by the auxiliary hood when in the operative position to flow to the incinerator for incinerating hydrocarbons or other combustible compounds present in the fume stream during operation of the incinerator.
 2. The fume treatment system of claim 1 wherein the furnace system is a tilting rotary furnace system, and the auxiliary hood is movable to the operative position over the furnace chamber mouth when the furnace chamber is in a tilted back position.
 3. The fume treatment system of claim 1 wherein the furnace chamber includes a door that is movable between closed and open positions for substantially closing and opening the furnace chamber mouth, the door having a flue through which the fume stream is emitted from the furnace chamber for collection by the auxiliary hood when the door is closed and the auxiliary hood is in the operative position, the auxiliary hood when in the operative position permitting movement of the door between the closed and open positions.
 4. The fume treatment system of claim 1 further comprising a cyclone in a flow path between the auxiliary hood and the incinerator for removing particulates from the fume stream prior to entering the incinerator.
 5. The fume treatment system of claim 1 further comprising a heat exchanger downstream of the incinerator for reducing the temperature of the fume stream exiting the incinerator, the fume stream blower being either upstream or downstream of the heat exchanger.
 6. The fume treatment system of claim 5 wherein the fume stream blower is downstream of the heat exchanger.
 7. The fume treatment system of claim 5 wherein there is a flow path from the heat exchanger to the main overhead hood for returning the fume stream exiting the heat exchanger to the main overhead hood for further processing.
 8. The fume treatment system of claim 7 wherein the returning fume stream from the heat exchanger is mixed with ambient air to further reduce the fume stream temperature.
 9. The fume treatment system of claim 1 wherein there is a flow path from the incinerator to the main overhead hood for returning the fume stream exiting the incinerator to the main overhead hood for mixing with ambient air and any fugitive emissions from the furnace chamber collected by the main overhead hood.
 10. The fume treatment system of claim 1 wherein the incinerator comprises a direct-fired afterburner including a burner assembly and a combustion chamber, further comprising a control unit for causing the auxiliary hood to move to the operative position over the furnace chamber mouth in response to the incinerator combustion chamber temperature reaching a first predetermined variable set point and for causing the auxiliary hood to move from the operative position to the inoperative in response to the incinerator combustion chamber temperature falling below a second predetermined variable set point that is below the first predetermined variable set point.
 11. The fume treatment system of claim 1 wherein the incinerator comprises a direct-fired afterburner including a burner assembly and a combustion chamber, further comprising a timer for starting the fume stream blower a predetermined time period prior to initiating ignition of the burner assembly for purging the incinerator combustion chamber before initiating ignition of the burner assembly.
 12. The fume treatment system of claim 1 further comprising means for modulating gas flow to the incinerator to maintain a predetermined temperature range in the incinerator during incineration of hydrocarbons or other combustible compounds in the fume stream.
 13. The fume treatment system of claim 1 further comprising a flow control valve for modulating the fume stream to the incinerator based on fume stream temperature downstream of the incinerator.
 14. The fume treatment system of claim 13 further comprising means responsive to an increase in the temperature of the fume stream downstream of the incinerator above a first predetermined set point to increase the amount of opening of the flow control valve and responsive to a decrease in the temperature of the fume stream downstream of the incinerator below a second predetermined set point which is below the first predetermined set point to decrease the amount of opening of the flow control valve.
 15. The fume treatment system of claim 14 further comprising means for causing the auxiliary hood to move from the operative position to the inoperative position in response to the fume stream temperature downstream of the incinerator rising above a third predetermined set point which is higher than the first predetermined set point.
 16. The fume treatment system of claim 15 further comprising means for shutting down the incinerator and the fume stream blower in response to the temperature of the fume stream downstream of the incinerator remaining above the third predetermined set point a predetermined time period.
 17. The fume treatment system of claim 1 wherein the incinerator comprises a direct-fired afterburner including a burner assembly and a combustion chamber, and control means for modulating fuel flow to the burner assembly to regulate the temperature of the combustion chamber.
 18. The fume treatment system of claim 17 wherein the control means includes means for reducing the amount of fuel flow to the burner assembly in response to the combustion chamber temperature rising above a predetermined first set point.
 19. The fume treatment system of claim 18 further comprising a flow control valve for modulating the fume stream to the incinerator based on fume stream temperature downstream of the incinerator, means for increasing the amount of opening of the flow control valve in response to the combustion chamber temperature rising above a predetermined second set point which is higher than the predetermined first set point after the fuel flow to the burner assembly has been reduced to a minimum, and means responsive to the combustion chamber temperature remaining above the predetermined second set point a predetermined time period for causing the fume treatment system to perform an incinerator over temperature emergency shutdown comprising at least one of the following: moving the auxiliary hood from the operative position to the inoperative position, shutting down safety shut off valves for halting the supply of fuel and oxygen to the burner assembly, and shutting down the fume stream blower.
 20. The fume treatment system of claim 1 further comprising a forced air heat exchanger downstream of the incinerator for reducing the temperature of the fume stream exiting the incinerator, and a control valve for modulating the flow of cooling air through the heat exchanger.
 21. The fume treatment system of claim 20 further comprising means for increasing the opening of the control valve to increase the flow of cooling air through the heat exchanger in response to the temperature of the cooling air out of the heat exchanger rising above a predetermined first set point and for decreasing the opening of the control valve to decrease the flow of cooling air through the heat exchanger in response to the temperature of the cooling air out of the heat exchanger dropping below a predetermined second set point which is below the predetermined first set point.
 22. The fume treatment system of claim 1 wherein the furnace system is a non-ferrous metal reclamation furnace system.
 23. A fume treatment system for treating a fume stream emitted from the mouth of a furnace chamber of a tilting rotary non-ferrous metal reclamation furnace system during charging and initial melting of a charge of scrap material containing the metal in the furnace chamber, the furnace system having a large main overhead hood located over the furnace chamber mouth, the fume treatment system comprising a retractable hood that is smaller than the main overhead hood, the retractable hood being movable between a first position overlying the furnace chamber mouth within the main overhead hood for collecting the fume stream emitted by the furnace chamber mouth during the charging and the initial melting of the scrap material within the furnace chamber and a second position spaced from the furnace chamber mouth, an incinerator in fluid communication with the retractable hood when in the first position, and a fume stream blower for causing the fume stream collected by the retractable hood when in the first position to flow to the incinerator where hydrocarbons or other combustible compounds present in the fume stream are incinerated during operation of the fume treatment system.
 24. The fume treatment system of claim 23 wherein the furnace chamber includes a door that is movable between closed and open positions for substantially closing and opening the furnace chamber mouth, the door having a flue through which the fume stream is emitted from the furnace chamber for collection by the retractable hood when the door is in the closed position and the retractable hood is in the first position, the retractable hood when in the first position permitting movement of the door between the closed and open positions.
 25. A method of treating a fume stream emitted from the mouth of a furnace chamber of a metal reclamation furnace system during a portion of the reclamation process, the furnace system having a main overhead hood located over the furnace chamber mouth, comprising the steps of positioning a second hood that is smaller than the main overhead hood over the furnace chamber mouth within the main overhead hood to collect the fume stream emitted by the furnace chamber mouth, and causing the fume stream collected by the second hood to flow through an incinerator where hydrocarbons or other combustible compounds present in the fume stream are incinerated.
 26. The method of claim 25 wherein the fume stream that is emitted from the furnace chamber mouth during charging and initial melting of a charge of scrap material containing the metal in the furnace chamber is collected by the second hood and caused to flow through the incinerator for incinerating hydrocarbons or other combustible compounds present in the fume stream, further comprising the step of moving the second hood to a position remote from the furnace chamber mouth during other portions of the reclamation process.
 27. The method of claim 25 wherein the furnace system is a tilting rotary furnace system, and the second hood is selectively positioned over the furnace chamber mouth when the furnace chamber is in a tilted back position.
 28. The method of claim 27 wherein the furnace system is a non-ferrous metal reclamation furnace system.
 29. The method of claim 27 wherein the furnace chamber includes a door that is movable between closed and open positions for substantially closing and opening the furnace chamber mouth, and the door has a flue through which the fume stream is emitted from the furnace chamber for collection by the second hood when the door is in the closed position and the second hood is positioned over the furnace chamber mouth, further comprising the steps of moving the door between the closed and open positions during times when the second hood is in position over the furnace chamber mouth.
 30. The method of claim 25 further comprising the step of causing the fume stream that is collected by the second hood when in position over the furnace chamber mouth to flow through a cyclone for removing particulates from the fume stream prior to flowing through the incinerator.
 31. The method of claim 25 further comprising the step of cooling the fume stream after the incineration step.
 32. The method of claim 31 further comprising the step of returning the fume stream to the main overhead hood after the cooling step.
 33. The method of claim 32 further comprising the step of mixing the returned cooled fume stream with ambient air within the main overhead hood.
 34. The method of claim 25 further comprising the steps of returning the fume stream to the main overhead hood after the incineration step, and mixing the returned fume stream with ambient air and any fugitive emissions from the furnace chamber collected by the main overhead hood.
 35. The method of claim 25 wherein the incinerator includes a combustion chamber, further comprising the steps of causing the second hood to move into position over the furnace chamber mouth in response to the temperature within the combustion chamber reaching a first predetermined variable set point and for causing the second hood to move away from the furnace chamber mouth in response to the combustion chamber temperature falling below a second predetermined variable set point that is below the first predetermined variable set point.
 36. The method of claim 25 wherein the incinerator comprises a direct-fired afterburner including a burner assembly and a combustion chamber, further comprising the steps of modulating gas flow to the burner assembly to maintain a predetermined temperature range in the combustion chamber during the fume stream incineration step.
 37. The method of claim 25 further comprising the step of modulating the fume stream to the incinerator based on fume stream temperature downstream of the incinerator.
 38. The method of claim 37 further comprising the steps of increasing the fume stream flow to the incinerator in response to an increase in the temperature of the fume stream downstream of the incinerator above a first predetermined set point, and decreasing the fume stream flow to the incinerator in response to a decrease in the temperature of the fume stream downstream of the incinerator below a second predetermined set point which is below the first predetermined set point.
 39. The method of claim 38 further comprising the step of moving the second hood away from the furnace chamber mouth in response to the fume stream temperature downstream of the incinerator rising above a third predetermined set point which is higher than the first predetermined set point.
 40. The method of claim 39 further comprising the step of shutting down the fume treatment in response to the temperature of the fume stream downstream of the incinerator remaining above the third predetermined set point a predetermined time period.
 41. The method of claim 25 wherein the incinerator comprises a direct-fired afterburner including a burner assembly and a combustion chamber, further comprising the steps of modulating fuel flow to the burner assembly to regulate the temperature of the combustion chamber by reducing the amount of fuel flow to the burner assembly in response to the combustion chamber temperature rising above a predetermined first set point.
 42. The method of claim 41 further comprising the steps of modulating the fume stream flow to the incinerator based on fume stream temperature downstream of the incinerator, increasing the fume stream flow in response to the combustion chamber temperature rising above a predetermined second set point which is higher than the predetermined first set point after the fuel flow to the burner assembly has been reduced to a minimum, and causing the fume treatment system to perform an incinerator over temperature emergency shutdown in response to the combustion chamber temperature remaining above the predetermined second set point a predetermined period of time. 